Looking for the Earth Next Door

Where is everybody? That’s the question physicist Enrico Fermi asked when realizing that the high probability of extraterrestrial life never matched any empirical observation. So far, no evidence of alien existence has been established on an exoplanet — a planet outside of our Solar System — this is why astrophysicists have been focusing on studying the diversity of planets and the habitability of other worlds. Mars is the closest candidate for a planet Earth #2, but what else lies outside of our Solar system?

How close are we to living on another planet?

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The Hall of Fame of exoplanets

Proxima Cen b

Travelling time

3.9 Lightyears

Gravity

1.01 x Earth

Surface Temperature

-9.3 Celsius

Radius

1.12 x Earth

Kapteyn b

Travelling time

11.7 Lightyears

Gravity

1.79 x Earth

Surface Temperature

-26.9 Celsius

Radius

1.64 x Earth

GJ 667 C c

Travelling time

20.4 Lightyears

Gravity

1.61 x Earth

Surface Temperature

13.3 Celsius

Radius

1.54 x Earth

GJ 667 C f

Travelling time

20.4 Lightyears

Gravity

1.39 x Earth

Surface Temperature

-14.3 Celsius

Radius

1.4 x Earth

GJ 667 C e

Travelling time

20.4 Lightyears

Gravity

1.39 x Earth

Surface Temperature

-46.0 Celsius

Radius

1.4 x Earth

TRAPPIST-1 g

Travelling time

36.3 Lightyears

Gravity

1.06 x Earth

Surface Temperature

-57.0 Celsius

Radius

1.13 x Earth

TRAPPIST-1 f

Travelling time

36.3 Lightyears

Gravity

0.61 x Earth

Surface Temperature

-43.4 Celsius

Radius

1.04 x Earth

TRAPPIST-1 e

Travelling time

36.3 Lightyears

Gravity

0.76 x Earth

Surface Temperature

-12.8 Celsius

Radius

0.92 x Earth

LHS 1140 b

Travelling time

37.4 Lightyears

Gravity

3.23 x Earth

Surface Temperature

-27.3 Celsius

Radius

1.43 x Earth

Kepler-186 f

Travelling time

516.0 Lightyears

Gravity

1.07 x Earth

Surface Temperature

-50.1 Celsius

Radius

1.17 x Earth

Kepler-1229 b

Travelling time

708.0 Lightyears

Gravity

1.39 x Earth

Surface Temperature

-21.7 Celsius

Radius

1.4 x Earth

Kepler-1652 b

Travelling time

756.0 Lightyears

Gravity

1.01 x Earth

Surface Temperature

-9.8 Celsius

Radius

1.12 x Earth

Kepler-442 b

Travelling time

1026.0 Lightyears

Gravity

1.3 x Earth

Surface Temperature

-2.6 Celsius

Radius

1.34 x Earth

Kepler-62 f

Travelling time

1104.0 Lightyears

Gravity

1.41 x Earth

Surface Temperature

-33.6 Celsius

Radius

1.41 x Earth

Methodology

All data comes from the exoplanet catalog of the Planetary Habitability Laboratory (PHL), retrieved on the 10th of October, 2018. Some data in this dataset are estimations calculated by the PHL, based on recorded data. For instance, the mass of many planets discovered by Kepler is defined by comparisons with mass classes of other exoplanets. The inner and outer edges of the Circumstellar Habitable Zones are also estimations.

The search for habitability by humans on an exoplanet is founded on Earth-like parameters (atmosphere, temperature, surface liquid water, etc.). Of course, this does not exclude the possibility of non Earth-like forms of life.